U.S. Pat. No. 6,752,036 B2 (JP-A-2004-513307) discloses a shift-by-wire control system including an electric motor for actuating a range switching unit. Specifically, the shift-by-wire control system detects an instruction shift range selected by an occupant of a vehicle, so that the electric motor actuates the range switching unit to switch a shift range of the vehicle in accordance with the instruction shift range. In a conventional shift-by-wire control system, a parking lock device brings an output shaft of an automatic transmission device to a lock state in conjunction with the range switching unit when switching to a P-range (parking range). The parking lock device also brings the output shaft of the automatic transmission device to a lock-release state in conjunction with the range switching unit when switching to a shift range other than the P-range.
In such a shift-by wire system, even when the electric motor cannot be supplied with electric power due to, for example, defect in a battery, the output shaft of the automatic transmission device is preferably brought to the lock state in order to park the vehicle. The shift-by-wire control system in U.S. Pat. No. 6,752,036 B2 is provided with a mechanical component such as a carriage, a lock member, a spring adapted to mechanically actuating the parking lock device, regardless of an electric power source.
However, in the structure of U.S. Pat. No. 6,752,036 B2, the parking lock device can be actuated regardless of a condition of the electric power source. Accordingly, the vehicle may be stolen, even when the vehicle is parked in a condition where the automatic transmission device is set at the P-range and is in the lock state. Specifically, the mechanical component of the parking lock device may be maliciously operated, and the automatic transmission device in the lock state may be brought to the lock-release state. In this case, the vehicle may be stolen.